CASTLE : THE HEREDITY OF SEX. 215 



11. Possibly the testis, in males of partheuogenetic species, contains 

 the male character as well as tlie female. If so, these are doubtless 

 segreo-ated in spermatogenesis, but only the female spermatozoa can be 

 functional, because only male fecundable eggs are produced by such 

 species. 



12. The segregation of sex-characters takes place in most partheuo- 

 genetic animals, and doubtless in dioecious animals also, at the second 

 maturation division (the " reduction division ") of the egg, and probably 

 at a corresponding stage in spermatogenesis. For (1) eggs which de- 

 velop without fertilization and without undergoing a second maturation 

 division contain both the male and the female characters, the former 

 recessive, the latter dominant; but (2) in normally partheuogenetic 

 species, eggs which, after undergoing a second maturation division, 

 develop without fertilization, are always male (except in lUiodites). In 

 such species the female character regularly passes into the second polar 

 cell, the male character remaining in the egg. In dioecious animals, 

 on the other hand, either sex character may remain in the egg after 

 maturation. 



13. In Hydatina senta there is no maturation division homologous 

 with the first maturation division of the eggs of other animals. A single 

 maturation division occurs in the male (or fecundable) eggs, but this is 

 clearly homologous with the second maturation division of other parthe- 

 uogenetic animals, for in it a segregation of sex-characters takes place. 

 In the female partheuogenetic egg, no maturation division occurs. 



14. The partheuogenetic egg of Rhodites rosae undergoes two matura- 

 tion divisions, but appai-ently without the occurrence of segregation in 

 eitlier of them. If segregation does occur in one of the two maturation 

 divisions, the character retained in the egg must be regularly the female, 

 because the offspring are uniformly of that sex. In that case, the geni- 

 tal gland of Ehodites probably develops, as does the testis of the honey- 

 bee according to Petrunkewitsch, from the fused polar cells. 



15. Abnormal sex-proportions among hybrids are capable of explana- 

 tion, in some cases, on the ground that certain combinations of gametes 

 are infertile. 



16. Sexual dimorphism, in a species, is the result of coupling, in 

 the zygote and in the gametes, of certain form-characters with one or the 

 other sex-character. A similar explanation accounts satisfactorily for 

 abnormal sex-distribution of the offspring, in the case of certain crosses, 

 between the two parent forms. 



